On Fri, 2015-10-02 at 14:45 +1000, Benjamin Herrenschmidt wrote:
On Fri, 2015-10-02 at 14:42 +1000, Dave Airlie wrote:
I don't think we resolved this the last time we talked about it,
but radeon writecombine maps fail hard on ppc, I think all the fixes either did something bad to AGP systems or weren't liked.
My patch attached just fixes radeon, which is where I'm still seeing the issue.
Yes, you MUST NOT set the flags of system memory to anything other than fully cachable on any cache coherent powerpc machine. This should be bolted into the DRM core imho.
_wc is only suitable for MMIO.
Note that I wouldn't be surprised if we weren't the only arch like that.
Playing with caching attributes of main memory smells from a system design and cache coherency protocol standpoint. x86 supports it but I wouldn't be surprised if some ARMs puke in interesting way as well.
Cheers, Ben.